Telephoto system



Sept. 26, 1939. F. .1. SOMERS TBLEPHOTO SYSTEM Filed larch 27, 1935 4Sheets-Sheet 1 RF. R./--. R. E ggizg BUFFER AMP 'AMP. AMP.

VISUAL MON! TOR 2 STAGE I2 0. c. AMP. AMP- AMP. FOR SYNC.

PULSES;

AB C D E F G H J K INVENTOR Sep t..26, 1939. F. J. SOMERS 2,174,490

TELEPHOTO SYSTEM Filad March 27, 1955 4 Sheets-Sheet 2 fig .3

INVENTOR. 90 FRANK J. SOMERS.

' ATTORNEYS.

Sept. 26 19392 F, SGMERS 2,174,490

TELEPHOTO SYSTEM Filed March 27, 1935 4 Sheets-Sheet 3 RAD/ RECEIVER IPULSE AMP.

Ago, [62 04: 2.1 I I63 r04 3;; 16% fig E2 {29 v Y; II, p y *MIIIIII. WII Y //8{ I I o I W {a a I AUTOMATIC vla 'z a fgk V. & FIX/N6 L0] I I LF. I 127 I r I V 3 STEP BYSTEP n wmiibfififl, .21 TRANSMITTER FRANK J.SOME RS ATT Patented Sept. 26, 1939 TELEPHOTO SYSTEM Frank J. somers,San Jose, Calif., assignor, by

mesne assignments, to Farnsworth Television & Radio Corporation, Dover,De l., a corporation of Delaware Application March'27, 1935, Serial No.iazss 9 Claims.

I My invention relates to a system for transmission of visualinformation at a distance and relates more particularly to a systemdesigned to transmit and receive images having several gradations oflight value.

Among the objects of my invention are: To provide a telephoto systemwherein transmission is satisfactory over a circuit or channel where thesignal-to-noise ratio may be as low as 2 or 3-1;

to provide a system adapted for the transmission and reception ofphotographs, drawings or the like, in so-called half-tone form; toprovide a system adapted for the transmission of photographs havingvarious degrees of light and shade; to provide inertia limitations; toprovide a telephoto system whereby enlargement or reduction may be madein the size of the reproduced image from that of the original picturefield; to provide a system for the transmission of photographs or otherhalf-tone reproductions to a distant point, utilizing the lower gradesof commercial channels, either wire or radio; to provide 'a system oftelephoto transmission having a minimum interfer- 5 ence factor; toprovide a telephoto system capable of operating at high speed; toprovide a telephoto system utilizing certain desirable characteristicsof a grid-controlled arc-rectifier; to provide a telephoto systemwherein amplitude changes during transmission have a minimum effect uponthe received image; to provide a telephoto-receiving system giving arecord in permanent form and a visual image simultaneously; to provide atelephoto-receiving system wherein photographs or other half-tones canbe made available at least in part immediately upon reception and bepreserved in recorded total form thereafter; to provide a telephotosystem utilizing desirable characteristics of cathode ray tubes; toprovide a simple and eflicient means and method of transmittingtelephoto images over wire or radio channels; to provide a" telephotosystem wherein the transmitted impulses are all of equal amplitudeirrespective of the degree of light and shade they represent; to providea telephoto system which can be operated over channels hitherto adaptedonly for facsimile transmission; to provide a means and method forselecting impulses of uniform amplitude from a heterogeneous train ofimpulses having varying magnitudes; to provide a means and method oftransmitting half-tone picture fields, which includes direct scansion ofthree dimensional subjects and reproducing said images and/or subjectsin the form of a multitone photographic record and as a visual picture atelephoto system having minimum therein.

simultaneously; and to provide a preferred telephoto system utilizing atleast in part certain desirable characteristics of any or all of theinventions disclosed and claimed in the following patents andapplications:

Patent N o.

Rutherford Issued Philo T. Famsworth 1,773,980 Aug. 26,1930 Philo T.Farnsworth 1, 970, 036 Aug. 14,1934

Serial No. Filed Farnsworth 270, 673 Apr. 17, 1928 Fernsworth 321,805Nov. 26,1928 Farrisworth and Lubcke. 449, 985 May 5, 1930 Farnsworth449, 98 May 5, 1930 461, 111 June 14, 1930 Dec. 4, 1930 550,653 July14,1931 614, 500 May 31, 1932 Farnsworth 664, Apr. 3, 1933 696, 994 Nov.1 7, 1933 and others.

Certain features herein disclosed are more fully described and claimedin my co-pending application, Serial No. 13,252, filed March 27, 1935,for

a facsimile system, the preferred embodiment of the present inventionutilizing some features in common with the preferred embodiment shown Myinvention possesses numerous other objects and features of advantage,some of which, gather-with the foregoing, will be set forth in thefollowing description of specific apparatus embodying and utilizing mynovel method.

Itis therefore to be understood that my method is applicable to otherapparatus,

and that I do not limit myself, in any way, to the apparatus of thepresent application, as I may adopt various other apparatus embodiments,utilizing the method, within the scope of the appended claims.

Referring to the drawings:

Figures 1 and 2, when combined, form a diagrammatic circuit reduced tolowest terms of a preferred form of telephoto transmitter employing myinvention. In order that the diagram may be conveniently followed in thebreak between the two figures, circuit connections common to the twofigures are lettered on each figure with corresponding characters from Ato K,

, inclusive.

Figure 3 is a diagram representing a preferred waveform for rectifieranode supply.

Figure 4 is a circuit diagram reduced to lowest terms of a preferredtelephoto receiver.

Figures 5 and 6 are diagrams representing the characteristic curves ofthe grid-controlled arc rectifiers, showing preferred steady biasingvalues.

Figure 7 is a diagram showing the preferred varying'bias values ofthearc-controlled rectifier.

In comparing telephoto transmission with facsimile transmission, it willbe found that telephoto is, in a number of respects, more complicated inthe equipment required. Defining the terms as herein used, telephototransmission comprises the transmission of an original picture field andthe reproduction of that field preferably and usually at a distantreceiving station in all orat least part of its intermediate shades orhalf-tones. 0n the other hand, facsimile transmission does not attemptto transmit partial values, but merely transmits the extreme contrastsof black and white. Telephoto, therefore, adds to the problem offacsimile the necessity of transmitting relatively fine variations ofamplitude due to closely adjacent shades in the original picture field,in addition to the extreme contrasts of black and white. The usualsystems of telephoto heretofore disclosed attempt to scan a picturefield with an aperture, the number of shades transmitted betweencomplete black and complete white being regulated by controlling thesize of the aperture. It has usually been thought desirable to make theaperture as small as possible, thereby securing a large number of valuelevels between the extremes of light and dark. This procedure leads to asignal train of extremely high frequency, and consequently, ifmodulatedon a radio carrier, leads to wide side bands, and the necessityfor wide channels; and if sent over a wire line requires special phasecorrection and other corrections well known in the art to prepare Iiihe(lline for the transmis' sion of a wide frequency Furthermore, suchprior telephoto transmission is based upon amplitude relations and thechannels not only require correction, but also require a signal-to-noiseratio of at least 20-1 for satisfactory transmission. My instantinvention, however. provides satisfactory telephoto transmission on aradio circuit or other channels where the signal-to-noise ratio is aslow as 2 or 3-1, and also utilizes signals of uniform amplitude.Consequently, a less expensive channel can be used,

as signals for telephoto transmission can be in the form of interruptedand successive uniform amplitude impulses, of amplitude modulation. Nosubstantial phase or frequency corrections are necessary, providing: theradio circuits and equipment are designed with ordinary care accordingto practices well known in the art. 7

I have found that there are certain desirable characteristics inherentin the Farnsworth system of electronic scanning, as exemplified,descrlfatd and claimed in the foregoing list of patents andapplications, for my new purpose will produce a preferred system whichis ideal for the transmission of telephoto images. It should be fullyunderstood, however, that 'I do not wish in any way to bev limited tothe use of the particular apparatus described by Farnsworth and otherslisted, and it is also to be understood that the actual apparatus usedis subject to design variations according to conditions to be met forany particular installaons.

thus obviating the necessity which, when combined and adapted In order,however, that the broader aspects of my invention may beunderstood,which can, as will be apparent to those in the art, be attained by theuse of other apparatus, I shall describe herein a preferred embodimentof apparatus to illustrate my invention comprising a complete system forthe transmission of telephoto images.

Broadly described, the circuit shown in Figures 1 and 2 is designed toprovide for the transmission of half-tone or variable shade pictureswithout the necessity of resorting to the usual method of continuouslyvarying the amplitude of the carrier in accordance with the varyinglights and shades appearing in the picture.

In my present system, it is only necessary to key the transmitter sothat all the impulses except those" used for synchronizing are of thesame shape, amplitude and duration. The pulses which are sent out may besquare-topped or rounded, it merely being required that they be uniform;

This method of transmission is obtained by scanning the picture in sucha way that the final signal impulses are all of the same length andduration but are sent on a time-distribution basis according to (a) thelight intensity of the individual elements which go to make up thepicture, and (b), their respective positions on the picture. In thisrespect, it should be understood that the word picture as herein used todescribe the picture field to be transmitted, may be either atwodimensional photograph or similar image, or it may be athree-dimensional subject, producing-a two-dimensional optical image ona scanning means.

In practice, the signal train may be obtained by a modification of theordinary method of scanning a picture a line at a time. In themodification, each line is scanned several times before going to thenext, and on each scanning of the same line, the transmitter sends outpulses representing picture elements of one range of light in; tensitiesonly. Thus, if each line isscanned five times, five different shades,ranging from black I way from the spirit of my'invention.

While it is true that the picture is in effect scanned several times forone transmission, when this method is used, the number of pictureelements transmitted during the scanning is not reater than that whichwould be obtained in the ordinary scanning method where variablemodulation is used, and the same tone grad tion is used.

The two main advantages of the system to be described are:

1. The equipment can be made to operate in cases where thesignal-to-noise ratio at the receiver is only 3-1 or less compared to aratio of 20-1 required for variable amplitude transmission;

2.-An ordinary radio transmitter such as is used for code messages canbe used as it is only .top of Figure 2.

far as transmission is concerned, a wire channel adapted to carry thekeying frequency is perfectly satisfactory, and the full equivalent of aradio channel. I I

In describing a preferred form of transmitter adapted for telephototransmission over a radio telegraph channel, I shall refer to Figures 1and 2, the two figures when combined, forming the complete -circuit. Thecircuit has been divided at the bottom of Figure land continued at theThe letters A to K inclusive indicate continuations of the same circuitconnection. In explaining my transmitter hereafter, the circuit will bedescribed as if it were joined into one complete diagram without furtherreference to the lettered breaks.

A picture field I represented in this case as being a photograph orsimilar field, but which may be any image or scene which is desired tobe transmitted, is'focused through a lens 2 on a photoelectric cathode 3of a dissector tube 4.

This dissector tube may be made in accordance with the teaching of theFarnsworth Patent No. 1,773,980, listed above, or may be the improvementthereon asshown, described and claimed in the Rutherford patent above.It comprises an envelope containing the cathode 3 at one end upon whichan optical image may be projected by the lens 2. As the cathode 3 isphotosensitive, electrons are emitted from the surface thereof inproportion to the intensity of the light striking the elementary areasthereof. A positive potential is applied from a dissector source'between cathode 3 and a target finger I placed close to the opposite endof the tube.

This target finger I is in the light path, but being of relatively smalldiameter and out of the focus of the optical system, it does not causedistortion but merely cuts down the total amount of light reaching thecathode by a small amount. Electrons emitted by cathode 3, therefore,are attracted by the positive potential towards the target finger I andare kept in parallel arrangement by the application to the tube of alongitudinal magnetic field created by a focusing coil 8 energized by afocusing source 9 under the control of a variable focusing resistor I0.The target finger 1 is provided with an aperture opening toward thecathode 3 through which electrons emitted from the cathode may pass tobe collected by. a target represented by a dotted line inside of thefinger 1 and being a continuation of\, the target lead II.

If the electrons in space are not diverted from their paths in the'tubeonly electrons from a of the cathode 3 will arsmgle elementary, arearive on the inner target, the remainder of the electrons being collectedby the outer target finger- I. Thus, there will be a difference in thenumber of electrons collected by the inner target and the outer finger,which will cause a current to flow through an output resistor I2 fromtarget source 6. If the electron beam is then deflected in twodimensions, the electron beamwill be scanned and will produce a train ofpicture signals in output leads I3, which will represent electricallythe picture field I.

Horizontal scanning is accomplished by the use of a horizontal scanningcoil I4 which is energized from a scanning oscillator assembly through ascanning secondary winding I5 applied to a core I6 of a transformerhaving a grid primary winding I1 and a primary plate winding I8 attachedto the respective grid and plate circults of an oscillator tube IS. Theconstants of the circuits attached to the oscillator tube I9 are soadjusted that tube I9 will self-oscillate, and also to supply a sawtoothcurrent to the secondary coil I5, consequently, to the horizontalscanning coil I4.

In order to completely scan the picture, it will be necessary to scanthe picture vertically as well. A vertical scanning coil is'thereforeprovided energized through leads 2| from a vertical scanning source 22which is in series with a variable resistor assembly 23 indicated asenclosed by the dotted line 23 in Figure 2. This variable resistorassembly, which may be called a progressive selector, controls theamount of current flowing through the vertical scanning coil 20 indecreasing equal increments.

The action of both the horizontal and vertical scanning is under thecontrol of a synchronizing assembly driven by a synchronous motor 24which drives a synchronizing rotor shaft 25 through reduction gears 26.The synchronizing shaft 25 carries thereon a four-cycle rotor 21 and atwenty-cycle rotor 28. The twenty-cycle rotor is provided with atwentycycle field 29 which is connected through leads 3!! to a controlprimary 30"on core I6 so that the scanning oscillator I9 is kept in stepwith the twenty-cycle frequency generated by the twentycycle rotor 28.

At the same time a four-cycle field 3I generates a pulse which is fed tothe input of a low frequency pulse amplifier tube 32, the output ofwhich passes through a low frequency pulse relay coil 33, the magneticpull'of which acts upon a low frequency pulse armature 34 to place upona first selector operating magnet 35, current from a selector battery36. Each impulse applied to the operating magnet 35 causes rotation offirst selector shaft 36' by one notch; thus changing the totalresistance of combined selector resistors 31, 38 and 39, At eachrevolution of the first selector shaft 36, contacts are made betweenfirst selector arm 40 and associated stationary contact 4| which directsa pulse from second selector battery 42 to second selector magnet 43,thus turning second selector axle 44 one notch. The process is repeatedto control the turning of the third selector axle or shaft 45 in asimilar manner. Thus, the entire range of resistance in resistors31-38-39 may be covered in successive steps and the number of stepsprovided in the assembly will of course correspond to the number oflines desired in scanning the picture from top to bottom.

It will be seen, however, that as the horizontal scanning is twentycycles; and the vertical scanning is on a four-cycle basis, that eachline will be scanned five times before moving on to the next line. Thisprocess repeats itself automatically so that at the end of each group offive sawtooth waves generated by the horizontal scanning oscillator I9,the selectors operate to move the electron beam to present the next lineto be scanned to the target aperture of the dissector tube.

The picture currents produced by this scanning process are passedthrough output resistor through a similar volume control 52.

amplifiers 41 and 48 have a different number of Thyratron, herein calledrectifiers for convenience. A rectifier 49 is connected to the output ofthe one-stage amplifier 4'! through a volume control 50, and the outputof the twostage amplifier 48 is connected to rectifier 5| stages, itwill be seen that the outputs of the two amplifiers are out of phase,the output of the one-stage amplifier 41 being applied to the grid 54 ofthe rectifier 49 in one direction and that of the two-stage amplifier 49applied to the grid 55 of the second rectifier II in the oppositedirection.

Rectifier 49, which receives the impulses from the amplifier having anodd number of stages is supplied with a positive steady bias by biasassembly 56, and rectifier 5| which receives its impulses from theamplifier having an even number of stages is supplied with a'negativesteady bias by negative bias assembly 51.

Theplates of the two rectifiers are energized by a two thousand-cyclerotor 59 attached directly to the shaft of the synchronous motor 24,this rotor creating two thousand cycle pulses in the main rectifieranode line 59, which passes through a common anode resistor 60 and thendivides at a connection 64 and is applied through a rectifier resistor62 to connect to anode 64 of the first rectifier 4.9, and through asimilar rectifier resistor 65 and connecting wire 66 to anode 61 of thesecond rectifier 5|. A connection 68 is made from the point where theanode supply.

divides to a keying resistor III. This keying resistor Ill is in serieswith the bias of an overbiased R. F. amplifier tube (not shown)contained in a radio transmitter assembly II comprising as an example, amaster oscillator. b fer, and three stages of R. F. amplification,radiating from the usual antenna system. Means for dverbiasing such anamplifier tube are well known in the art.

The keyingresistor I0 is placed in the circuit of the R. F. amplifierstage so that when current is passed through the resistor betweenconnection 68 and ground 12, the voltage generated by this current willoppose the bias of the amplifier tube, thus reducing the bias andallowing the radio transmitter to operate. When no current is flowingthrough resistor III, the bias 'on the radio frequency amplifier blocksthe transmitter and no signals will be radiated. The complete operationof this circuit will be explained separately.

In addition to applying certain signal variations to a radio transmitterthrough the circuits just described; I also prefer to transmit asynchronizing pulse. I, therefore, take energy from the twenty-cyclealternator combination 28-28 which is present in leads 30, and apply itto an amplifier input circuit ll to amplify the synchronizing pulses.The amplified pulses are passed through a synchronizing pulse connection"to the resistor" opposite the grounded end. The output of thisamplifier passes through resistor 10, and these pulses change the biason the R. F. amplifier to cause the transmission of the horizontalsynchronizing pulse.

Furthermore, in addition to the steady bias on the rectifier tubes 49and 9| provided by biasing assemblies 56 and 51, I prefer to provide anadditional varying bias, more particularly, a bias that will vary'eachtime an individual line is scanned. This varying bias is provided byplacing on the end of the rotor shaft 25 a cylinder '9 having five equalcircumferential portions of Asthedifferent light transmission values sothat a slit 8| positioned outside of the transparent cylinderwill'receive five different light values from axially positioned exciterlamp 92. The light passing through the slit' is directed on aphotoelectric cell 83, the output of which'is applied to a pair of grids94 and 85, connected in parallel, of a pair of amplifying tubes 86 and81. The outputs oftubes 86 and 91, which appear as voltage drops acrosstheir respective plate resistors 88 and 89, are applied to the grids ofthe rectifiers 49 and SI in opposite polarity. x

The photoelectric cell 83 is energized by a cell source 90 connectedacross a cell resistor 9|, one end of which is connected to grid 84 ofamplifier tube 86, the other end being connectedto the cathode 92 ofamplifier tube 81. Thus, the varying bias of the two 'rectifiers 49 and5| will depend upon the value of the transparency presented to thephotoelectric cell, the general action being discussed later.

The operation of the dissector 4 in general, as far as the scanning isconcerned, is unusual only in that each line is scanned five times. Thepicture currents produced by the scanning process are represented by thevoltage dropv across the output resistor 12 and these voltages afterbeing amplified, are applied to the inputs of amplifiers 41 and 48, oneof which is a single-stage, and the other a two stage amplifier. Theoutputs of these amplifiers are fed to the grids of the two rectifiertubes 49 and SL Rectifier 49 has a steady positive bias on its grid andrectifier 5| has a steady negative bias on its grid. With thisarrangement, the signal applied to the rectifier grids comprises aseries of picture impulses whose heights are proportional to the lightintensity of the picture elements being scanned, but due to the factthat the signals applied to rectifier 5| pass through an even number ofstages, the pulses applied to it are of opposite polarity to thoseapplied to rectifier 49 which receives its signal, through an odd numberof stages. Therefore, a signal which decreases the instantaneousnegative bias on the grid 55 for rectifier 5|, tending to make itsbreakdown voltage lower, willincrease the instantaneous nega-- tive biason grid '54 on rectifier tube 49 which has a steady positive bias, whichtends to prevent it from breaking down. It'is believed that cyclegenerator, their breakdown is controlled by ,the grid voltage which iseffective at the beginning of each positive half-cycle of the twothousand-cycle supply. By adjusting the resistors in the respectivebiasing assemblies 56 and 51, the rectifiers can be givena steady biassuch that neither tube will fire when the signals due to a picture beingscanned are within a given range for values corresponding to a givenrange of light intensity on elementary areas in the picture. Whenneither tube fires, the voltage drop across the keying resistor III is,such that on the positive halves of the two thousand-cycle supply thevoltage is sufiicient to unblock the grid of the radio frequencyamplifier in the transmitter and cause signals to be transmitted by theantenna attached thereto.

If. either rectifier tube 49 or ii fires or if both rectifiers firetogether. the voltage drop fore not available in resistor to create-avolt- If, however, either one of the tubes is passing current, currentwhich flows through resistor I0 is used in one or both of the tubes andis thereage sufficient to unblock the amplifier grid. It is, therefore,seen that the two rectifier tubes together can be controlledto operatethe radio transmitter only when they receive signals corresponding to agiven level or range of light intensities. I

The manner in which these two rectifier tubes operate to control theradio transmitter and release energy therefrom only for picture elementswhich lie within a given range of light intensity can best be explainedby reference to a specific numerical example, and reference will also behad to Figures 5 and 6, which show the grid voltage-firing voltagecurves of the two rectifiers, plotted one above the other and to thesame scale, Figure 5 representing tube 49 and Figure 6, tube 5|.

Let us assume that the alternator voltage is two hundred volts peak attwo thousand cycles. Since I prefer to design the alternator to supply acurrent having a waveform substantially fiattopped and substantiallyperpendicular sides as shown in Figure 3,-there will be no operation ofthe rectifiers except under the condition of full two hundred voltsapplied anode voltage. For a full platevoltage of two hundred volts, thenegative grid bias must be more than twentyone volts to prevent the tubefrom firing. Continuing with the numerical example, let the steadybattery bias on rectifier 49 supplied by bias assembly 56 and the dropacross resistor 89 be +10 volts and the steady bias applied to rectifiertube 5| by means of the bias assembly 51 and the drop across resistor 88be 53 volts.

' It will thus be seen that'when no picture signal is supplied,rectifier 49,

whose grid has a bias thirty-one volts more positive than the criticalvalue of 21 volts required to stop the. discharge, will fire on everypositive pulse supplied On the other hand, rectifier tube 5| has a biaswhich is thirty-twovolts more negative than that required to preventdischarge and, therefore, it remains inoperative as long as there is nopicture signal.

As already explained, the picture signal is fed to the rectifiertubesthrough twoseparate amplifiers, one having an odd and the other aneven number of stages. Therefore, a picture element which tends toincrease the effective negative bias on tube 49 will decrease theeffective negative bias on tube 5|. 1

Let us assume that we are scanning a line of the picture, and we wish tosend out signal pulses only for picture elements which will producesignal voltages between thirty-one and thirty-two ,volts." Referring toFigures 5 and 6, rectifier tube 49 has a steady bias on it of +10 voltsand rectifier tube 5| has a steady bias of 53 volts. During any: onescanning line the drops across resistors 89 and 88 remain constant.

"Applying diiferent'values of signal voltages, we find the following:(a) A signal of 31.1 volts makes the effective .bias on rectifier 1 1 b?-2 WM, 59 t at this tube cannot fire. The same signal at the same timereduces the effective bias on rectifier "tube 5| to 21.9 volts so thattube 5| is also inoperative. Under these conditions, the voltage dropacross the keying resistor 18 is sufficient to unblock the R. F.amplifier and cause the radio transmitter to send out signal impulses.(b) It can be shown similarly that tubes 49 and 5| will also beinoperative for signals lying between 31.1 and 31.9 volts and the radiotransmitter will therefore operate in this range.

(0) If the picture signal drops below 31 volts,

say to 30.9, the effective bias on tube 49 will be 20.9 volts and tube49 will therefore fire and consequently, the radio transmitter willremain inoperative. At the same time, the bias on tube 5| will be -22.1volts and it will not fire; but this is immaterial because radiotransmission is prevented due to tube 49 firing.

(d) If the picture signal increases above 32 volts, say to 32.1 volts,the radio transmitter will be inoperative again because while rectifiertube 49 will then have a bias. of 21.1 volts which will prevent itsfiring, tube 5| will fire due to its bias having been reduced to -20.9volts which is less than the critical value. It is, therefore,

seen that for given values of steady bias the rectifiers can be made tooperate in such a way that the radio transmitter is energized only forpicture elements having light intensities which 'of the rotating filmcylinder 88.

For example, to cause the transmitter to operate .for picture elementsdelivering 10 to 11 volts to the rectifier grids, the transparentfilmfor the scanning line in question is set to cause the photoelectric cell83 to operate to pass 'sufflcient current to make the sum of the dropsacross resistor 89 and the bias value placed on the grid 54 of the tube49 by the biasing assembly 56, to be --11 volts. At the same time, thedrop across resistor 88, together with themes supplied by bias assembly51 to tube 5| will become -32 volts; thus the range of light intensitieswhich can cause the radio transmitter to operate is automatically setfor each repeated scansion of the same scanning line by thedrum'carrying the transparent film, and its associated photoelectriccell, which, operating through amplifier tubes 84 and 85 fix the varyingbias of the rectifiers.

It should be noted that the grid bias voltages controlled by thephotoelectric cell 83 are applied to the rectifiers through separateamplifier tubes 86 and 81. The outputs of thesetubes, which appear asvoltage drops across their plate resistors 89 and 88, are applied to thegrids of the rectifiers in opposite polarity. It should also be notedthat the characteristic curves of straight lines. While this linearityis a fortunate circumstance in that it makes for an easy ad therectifiers are the rotating drum are arranged in orderly manner so thatthe bias provided to the rectifiers 49 and starts in at a low value forthe first scanning of a line and ends at a high value at cell 83, whenplotted on a time basis is shown in Figure 7.

By proper selection of transparencies for the I rotating drum 80 and byadjusting the steady bias assembly 56 and 51, it is possible to obtainany desired range of light values for each scansion' and. it is quiteobvious that certain shades may be accentuated if desired. In otherwords, the selection of the five different values need not necessarilydiffer byequal values and any arrangement may be made which will suitthe subject matter best. However, for the five scannings of 'the sameline, we may adjust these values so that the radio transmitter isoperating for example, as follows: i

In scanning a given line:

First scanning Transmit signals for picture elements producing 0 tom gvolts Second scanning 10 to 20 volts Third scanning 20 to 30 voltsFourth scanning to volts Fifth scanning 50 to volts It is obvious thatthe grouping of voltages referred to above is that which might be givenwhen an object was scanned five times, but it should be pointed out thatmy system as described is not limited to any particular number ofscannings of a single line and that if a greater number of scannings ismade, the range of voltage for the picture elements on a single scanningwill be less and for a lesser number of scannings the range willpreferably be greater. It is possible, however, because of the extremesensitivity-of the arc-controlled rectifiertube to reduce the range to afraction of a volt where a single line is being scanned at large numberof times in order to obtain extreme detail.

As explained above, a pulse amplifier is provided which is connected tothe scanning oscillator l9 and to the;keying resistor 10 to send out asynchronizing pulse at the end of each traversal of a line. f'rnepolarity of the syn hronizing pulse and the intensity are such as t;completely unblock the radio frequency amplifier in the same manner asthe pulses produced by the two thousand-cycle generator, and to causethe radio transmitter to send out a synchronizing signal at the end ofeach traversal of the field by the scanning aperture. This signal isadjus ed preferably to be of-a length corresponding to ten per cent ofthe,

period of scansion of one line, which for thep'resent example would beten per cent of .05 second, or .005'second. The synchronizing pulse is,therefore, ten times as long as any one of the two thousand-cyclepicture pulses sent out by the transmitter and can therefore be readilyseparated from these picture pulses at the receiving end by a simpleresistance-capacity filter, as will be later described. It is also anadvantage to make the corners of the synchronizing pulses rounded tofacilitate separation from the signal at the receiver and this may bedone by control of the amplifier waveform as is well lmown in the art.

The descriptionabove given completes the 011.-

cuits and operation thereof in the complete telephoto transmitter. Iprefer, however, in order to check the operation of the transmitter toutilize a visual monitor assembly 95 for picking up the radio spacecurrent in a miniaturereceiver so that proper adjustment'may bemaintained on the transmitting device. This is in accordance with allmodern practice andthe general operation of the visual monitor will besimilar to that oi the receiver about to be described, with theexception that it may be possible, if desired, to utilize synchronizingpulses taken directly from the main transmitter.

At the receiving end, a preferred example of which is indicated by thediagram comprising Figure 4, the output of a radio receiver lllil ofordinary design is in the form oi pulses grouped in accordance with thepicture signals. This form of output has been described fully in mycopending application referred to above and is obtained by the use of anarc-controlled rectifier tube similar to that used in the transmitter,but preferably having an anode excitation of around five thousandcycles, the grid being controlled by the amplified and rectified radiosignal. This particular type of receiver output is used in order thatthe signal-to-noise ratio may" be low and that the signals be separatedfrom the noise which would ordinarily accompany it, due to the sharpselection of amplitude inherent in the operation of a grid-controlledrectifier. In other words, the output is composed of a series of uniformamplitude, five thousand-cycle waves, the grouping of the seriescorresponding to the value of the picture impulses being transmitted.

This grouped signal is passed through an output resistor IM and fed.through a grid connecnon-I02 to the control grid I02 of a visual monitorcathode ray tube I03 which preferably has a fluorescent'screen having aconsiderable time lag light therefrom is focused on a moving film I06or' sensitized paper which after being exposed is passed into anautomatic developing and fixing bath l 01 to emerge as thefinished'product.

Both cathode ray tubes are thus simultaneously energized. 'At the sametime part of the output of the radio receiver is conducted throughconnection I08 to a synchronizing amplifier tube I09. The picture pulsesare prevented from operating or influencing this synchronizing amplifierby means of a low pass resistance-capacity wave filter comprising acondenser H0, and resistor III, a series capacity H2 and a grid resistorIII, which descriminates against rapid steep sided picture pulses andpasses the rounded synchronizing pulses. The synchronizing pulse thenappears alone in the anode circuit H5 of the synchronizing amplifier andcontrols, as in the transmitter, the output of a receiving lateralscanning oscillator 6, the output of which is passed through transformerH1, through leads .8 to thedateral scanning coil H8 of receiver cathoderay tube I05, and also to monitor tube .45 This cathode ray' tubepreferably has an instantaneous screen and the .winding i22 has I22.This relay will, therefore, operate once for every five cycles producedby the twenty-cycle scanning generator H6. The relay operated by movablearms, one of which, selector arm I24, is connected in series with athree-step-by-step selector I operating exactly the same as that shownenclosed in the dotted line 23 of the transmitter drawing in Figure 2.The output of this step-by-step selector is applied to the verticalscanning coil I26 of the receiver cathode ray tube through a supply lineI21 and also to monitor tube I03 as indicated by a broken circuit X-X.The other arm I21" normally closed, controls the current from a relayassembly source I29, which is the main supply for a series of lockingrelays which operate to change the effective resistance of'a maincathode ray tube by a resistor I30. The drop across this resistor isapplied to a beam bias grid I30 of the visual monitor I03 through leadI3I and to the beam bias grid I3I' of the receiver cathode ray tube bylead I32.

In order to reproduce'in the receiver tubes the various shades appearingin the transmitted picture, it is desirable to change the bias on thecathode ray receiving tubes to a different steady value for eachrepeated traversal of the same scanning line, and todo this insynchronism with the rotation of the transparencies which operate therectifier bias supplies at the transmitter. This is readily done byrelay arms I40, I, I63 and I44 connected to short portions of the biascontrol resistor I30. The relays carrying the so that the bias of thethe relay gaps are open. At the end of the first scansion of a givenline at the transmitter a-p0rtion of the output of the lateral scanningoscillator H6 is picked up by a pulse winding I45 on transformer I I1and passed through a pulse amplifier I46. The amplified pulse is appliedto the operating winding I41 of the first relay thus operating therelay, shorting out a portion of the resister I30, and at the same timedrawing down a locking arm I48. The bias is thus adjusted for the secondscansion of the same line.

The actuation of the locking arm I48 closes a connection with a lockingwinding I49 of the I first relay, the current passing also through anoperating winding I50 of a first delay relay. Thus, the first bias relayis locked. In series parallel with winding I50 of the first delay relayis a condenser I5I which must charge before the first delay relay canclose, and its value is made such that this relay does not close untilafter the pulse from the pulse amplifier has operated the first biasrelay and then dropped to zero. After the pulse passes, and condenserI5I charges, winding I50 of the first delay relay becomes energized,closes a connection I50, hifting the out put of the pulse amplifier I46to winding I52 of the second bias relay. The pulse-thenoperates bias armI4I shorting another portion of resistor I30 and also operating lockingarm I53, which latter arm closes the circuit to a delay winding I54 of asecond delay relay.

The winding I54 is also shunted by a capacity I55, which delays theoperation oi this relay until the pulse has passed, whereupon thecurrent ,passing through the winding I54 will operate transferlarm I55and locking arm I56 which again transfers the output of the pulseamplifier to operating winding I51 of the third bias relay which in turnoperates the bias arm I43 to short out still another portion of resistorI30, and operates locking arm I50 which closes the circuit and transferscurrent to the energizing winding I60 of the last bias relay winding I64which in turn operates the bias arm I44 to short out the remainder ofthe resistor, and lock the bias relay. All or the delay relays havelocking windings and remain closed during the progressive shorting ofresistor At the end of five scannings of the same line at thetransmitter, the receiver multivibrator actuate's tube I2I and relayI22. This relay opens all the lock-up windings, releasing .all of therelays andalso operates the step-by-step selectors so that the spots ofthe cathode ray tubes are moved down ready for the next scanning line.The cycle isthen repeated.

The four bias relays should be capable of closing in about .005 second.The three transfer re- I lays, by having the condensers shunt them; arearranged to be time delayed by about .03 second after the operatingvoltage is applied. Relays for these speeds do not present any newproblems as high speed relays operating much faster than this areavailable. However, I do not desire to limit myself to this particularmethod as many other means for effecting the desired bias changes forthe cathode ray tubes will occur to. those skilled in the art.

For example, a synchronous motor carrying a set of transparencies and aphotoelectric cell such as that used at the transmitter might besubstituted for the relays at the receiver or a series of arc-controlledrectifiers might be used. The apparatus describedfor this bias change isin itself no part of the instant invention and is simply used as anexample of a means.

It can therefore be seen that the spot of the receiver cathode ray tubetravels in synchronism with the scanning at the transmitter, that thetransmitter scanning aperture traverses thesame line several times, andthat a pair of arc-rectifier tubes causes picture elements of differentintensity ranges to be picked out, separated and transmitted during eachrepeated scansion. v The signals thus produced key the radio transmitterso as to send out signals in the form of dots of uniform length, andshape, and a relatively longer corresponding to intensity of pictureelements being transmitted, for each scansion. The receiver is alsoprovided time lag screen and a cathode for automatic photographicrecording.

The receiver is enabled to operate under conditions of relatively poorsignal-to-noise ratio -2 or 3 to 1--because its output tube is agridcon'trolled rectifier whose platev supply is fed by a fivethousand-cycle a. 0. source. The bias of this grid-controlled rectifieris adjusted so that it operates for the peak voltage of the signal, and

with a visual monitor having a ray tube arranged noise of less intensitythan the signal does appear in the picture.

I claim:

1. The combination with an electron image dis-=- sector of ,a telephototransmitter comprising a picture field within said electron imagedissector, means for scanning a portion of said field a plurality oftimes within said image dissector to produce a picture signal before theremainder is scanned, a signal transmitter, and means for changing theresponse of said transmitter to said signal in accordance with differentlevels thereof at each successive scansion of said portion.

2. The combination with an electron image dissector of a telephototransmitter comprising a picture field within said electron imagedissector, means for scanning each line of said field a plurality oftimes to produce a picture signal before scanning the next line, asignal transmitter, and means for changing the response of saidtransmitter. to said signal in accordance with different amplitudelevels thereof at each successive scansion of said line.

3. The combination with an electron image not dissector of a telephototransmitter comprising a picture field within said electron imagedissector. means for scanning a portion of said field a plurality oftimes to produce a picture signal before the remainder is scanned, asignal transmitter, means for changing the response of said transmitterto said signal in accordance with different levels thereof at eachsuccessive scansion of said portion, means for scanningremainingportions in like manner, and means for transmitting asynchronizing signal between each successive scansion of all theportions.

4. The combination with an electron image dissector of a telephototransmitter comprising a picture field within said electron imagedissector,

means for scanning each line of said field a plurality of times toproduce a plurality of substantially identical successive trains ofsignals representing a single line before scanning the next line; asignal transmitter, means for selecting impulses within a diflerentpredetermined amplitude range fromeach of said identical trains, andmeans for keying the transmitter by the selected signals.

5. The combination with an electron image dissector of a telephototransmitter comprising a picture field within said electron imagedissector, means for scanning each line of said field a plurality oftimes to produce a plurality of substantially identical successivetrains of signals representing a single line before scanning the nextline, a signal transmitter, means for selecting impulses within adifferent predetermined amplitude range from each of said identicaltrains, means for grading the average levels of said ranges inaccordance with the gradations of light and shade of said field it isdesired to transmit, and means for keying the transmitter by theselected signals.

' 6. The method of telephoto transmission which comprises scanning eachline of a. picturefield a. plurality of times to produce successivesubstantially identical trains of picture impulses before Y scanning thenext line, selecting from each of" beam in accordance with the saidtrains impulses within a diflerent predetermined amplitude range,transmitting the selected impulses, repeating the steps on succeedinglines,

' receiving said signals, creating a beam of electrons, modulating saidbeam. by said signals,

' changing the average response of said beam by a differentpredetermined amount for each successive scansion of the same line,repeating the steps on succeeding lines, creating a visual indication ofthe strength of said beam, moving said scansion at the transmitter, andphotographing said visual indication.

7. The method of telephoto transmission which 1 comprises scanning eachline of a picture field a plurality of times to produce successivesubstantially identical trains of picture impulses before scanning thenext line, selecting from each of said trains impulses within adifferent predetermined amplitude range, transmitting the selectedimpulses, repeating the steps on succeeding lines, receiving saidsignals, creating a pair of electron beams, modulating both of saidbeams by said v signals, changing the average response of said beams bya diiferent predetermined amount for each successive scansion of thesame line, repeating the steps on succeeding lines, creating a,persistent'visual indication. of the strength of one, of said beamscreating a transient visual indication of the other of said beams,moving said termined amplitude range, transmitting the se-' lectedimpulses, repeating the steps on succeeding lines, receiving saidsignals, creating a beam of electrons, modulating said beam by saidsignals, changing the average response of said beam by a differentpredetermined amount for each successive scansion of the same line, saidamounts being changed to correspond to the amplitude range selection atthe transmitter, repeating the steps on succeeding lines, creating avisual-indication of the strength of said'beam, and moving said beam inaccordance with the scansion at the transmitter. v

9. The combination with an electron image dissector of a telephototransmitter comprising a picture field within said electron imagedissector, means for scanning each line of said field a plurality oftimes to produce a plurality of trains of signals representing a singleline before scanning the next line, a signal transmitter, means forselecting impulses within a predetermined amplitude range from each ofsaid trains, means for cyclically varying the response of said signaltransmitter to diiferent impulse levels on succes- FRANK J. SONIERS.

